Compositions which are curable to give elastomeric silicone foams are known in the art. In order to prepare foams of this type, curable compositions are treated with blowing agents which decompose when heated with the evolution of gas and thus effect foaming of the compositions during the curing reaction. In this regard, reference may be made to, for example, U.S. Pat. No. 2,857,343, U.S. Pat. No. 5,019,295 and GB-A 1,130,674.
In the curing reaction based on diorganopolysiloxanes containing Si-bonded vinyl groups and diorganopolysiloxanes containing Si-bonded hydrogen atoms, which reaction is catalyzed by platinum or platinum compounds, hydrogen is evolved as the blowing agent gas, which facilitates foaming, by the addition of water, organic alcohols or diorganopolysiloxanes containing Si-bonded hydroxyl groups. In this context, reference may be made to U.S. Pat. No. 4,189,545, U.S. Pat. No. 4,613,630, U.S. Pat. No. 4,871,781 and EP-B 227 233.
According to EP-B 97 915 and U.S. Pat. No. 4,391,765 an elastomeric foam is obtained by mechanical production of a foam from an aqueous, reactive silicone emulsion, adding surfactants and thickeners, in order to render the foam stable until the water is removed, and subsequent drying of the foam in an oven or in air, or subsequent exposure of the foam to an amount of microwave energy sufficient to remove water.
U.S. Pat. No. 4,584,324 discloses a pressurized composition comprising an aqueous emulsion which contains a crosslinking silicone polymer, emulsifier, water and optionally filler, crosslinking agent and thickener and which on drying at room temperature cures to give an elastomeric film and sufficient aerosol blowing agent, such as nitrogen, nitrogen oxide, isobutane, propane, dichlorodifluoromethane or trichlorofluoromethane, to convert the composition into a foam if it is reduced to atmospheric pressure at 25.degree. C. The resultant foam yields an elastomeric foam after removal of water. The object of the invention was to provide water-based blowing agent compositions suitable for the preparation of elastomeric silicone foams. A further object was to provide compositions which are curable to give elastomeric silicone foams and which do not contain any toxic blowing agents or blowing agents liberating toxic decomposition products.